Transport in Plants

Question 1

xylem and phloem

Answer 1

• Xylem: Transports water and minerals from roots to leaves and other parts of the plant (transpiration). Xylem are made up of hollow dead cells, joined end to end. Xylem vessels contain no cytoplasm or nuclei, their walls made up of cellulose & lignin to help keep plants upright. Found towards top of vascular bundles.
• Phloem underneath xylem in vascular bundle. Phloem is an elongated tubular shape with thin walled sieve tube elements. They do not contain cytoplasm, no nucleus and do not hav lignin in walls. Phloem transports food and nutrients such as sugar from leaves, sucrose and amino acids (translocation).

Question 2

Root hair cells

Answer 2

Water taken up by root hair cells by osmosis. They are adapted to having efficient water uptake by having large surface area, which increases rate of osmosis In the root. As well as increase rate of ion uptake by active transport. They also have thin walls, so diffusion distance is shortened.

Question 3

Pathway taken by water through root, stem and leaf as root hair cell, root cortex cells, xylem and mesophyll cells

Answer 3

Water taken up by root hair cells by osmosis. Water moves into root cortex cells via osmosis (root hair cells have have higher water potential than cortex cells), before entering xylem vessel where it is drawn up the stem to the leaves. At leaf it diffuses into mesophyll cells, where it is used in metabolic reactions such as photosynthesis.

Question 4

water is transported from the roots to leaves through the xylem vessels

Answer 4

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Question 5

Transpiration

Answer 5

loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata

Question 6

how water vapour loss is related to the large surface area of cell surfaces, interconnecting air spaces and stomata

Answer 6

• Transpiration is the loss of water vapor from mesophyll cells due to evaporation. water vapor exits plant through stomata. Water helps maintain plant structure by keeping cells turgid.
• If plant looses too much water, that is not replaced, it begins to wilt. As water moves out the cells and turgor pressure decreases. to limit water loss, plant closes stomata to prevent water vapor diffusing out.

Question 7

mechanism by which water moves upwards in the xylem

Answer 7

Water molecules moves up xylem by transpiration pull ( not osmosis), Water molecules are cohesive, meaning they stick together. This means water evaporates at the leaf and diffuses out of the stomata, more water is drawn up the plant from the roots.

Question 8

Explain the effects of variation of temperature

and humidity on transpiration rate

Answer 8

Rate of transpiration depends on the humidity and temperature. On warm days temperature is higher, so water evaporates more easily, therefore there is more diffusion of water vapor out of the plant, thus rate of transpiration is high. A high humidity, however, decreases the rate of transpiration as concentration gradient of water vapor between inside and outside the plant Is comparatively low, so diffusion out the plant is slower.

Question 9

Translocation

Answer 9

The movement of sucrose and amino acids in phloem from regions of production (source) to regions of storage, or to regions where they are used in respiration or growth (sink)

Question 10

some parts of a plant may act as a source and a sink at different times during the life of a plant

Answer 10

• Sucrose and amino acids are produced in the leaves, before being transported to the roots for storage. They are later transported to regions where they are used in respiration and growth.
• Some parts of the plant, such as leaves, can act both as source and sink, as they synthesis molecules and use them in metabolic reactions.